To remove your own armor in normal mode (as opposed to hyper mode) use the following move: f, b, f, b + P + K + G. This move is very tricky to work at first because the timing is delicate, but the effect is worth it.

To activate the big heads option in the Options Plus menu, you must fight 100 matches in the VS or Arcade modes.

To access Honey's bonus outfits, defeat the game on the Very Hard setting in Arcade mode. These outfits are selectable in Vs., Training, and Team Battle modes.

To activate the invisible walls option in the option plus menu, you must succesfully perform 350 MOVES in the training mode.

To play the the smaller version of the end boss, you must win the game with any character in normal mode.

To get Pepsi Man in the Japanese version of Fighting Vipers all you have to do is let Bahn (your first opponent), beat you up. Don't do anything; just let him kill you.